In November 2011 we published a review of the Spanish Neutral Audio X-DREi, a so-called after preamp. During the actual review period we couldn't fully grasp what the DREi technology hidden inside a sealed container of the X-DREi was really about. It left of us in a state of bewilderment which only recently cleared up a bit. When inserted between pre and power amp, the X-DREi splits the signal into three copies to be rendered as sine, triangle and square waves respectively to which analog processing is applied before all three copies are recombined again into the output signal.

Clearly DREi short for dynamic reduction of electronics interaction is a type of filter or analog signal processor. By reshaping the three different wave shapes, the resultant signal is said to be cleaner and more intelligible. After that review we'd spent more time with the device to conduct further experiments. This led us to conclude that the secret circuit of Jose Manuel Jimenez is in fact a multi-band processor involving deliberate phase manipulations. Today affordable digital audio work stations called DAW can master music tracks without ever setting foot in a proper recording studio. Whereas in the 'olden' days engineers often went to great lengths to control the phase alignment of their hardware and track splices, Pro Tools can ride roughshod over it all by combining its various edited signal layers with a plug-in. Presto, perfection. Or is it?

Humans are very sensitive to phase relationships embedded in the harmonics. Phase rotations between the various overtones relative to their fundamental lead to timbre shifts and imaging artifacts which we notice as distortion or a sense of obfuscation or opacity. It's in this precise domain where the X-DREi's phase alignment seems to work. In its signal processing it also seems to address intermodulation distortion between closely spaced frequency events where two pure tones of say 3'000Hz and 4'000Hz generate 'aliases' at 2'000 and 5'000Hz. These are distortion products which show up as small spurs in a graph. As non-musical artifacts our hearing is quite sensitive to them. The obvious challenge is how to identify which elements of the signal are embedded distortion to remove them when the already contaminated signal itself has to be used as its own reference.

Against this backdrop of a tad more insight into the undisclosed X-DREi processing math, Neutral has introduced a simpler version of their technology. Instead of a preamp-follower component, the Spaniards now have an interconnect with built-in DREi module. Their catalogue already had copper and silver wires—bi-metal cables in their parlance—to lead quite naturally to such a hybrid product just as makers of powerline filters and power cords sooner or later develop a cord with a built-in filter. Because any DREi module relies on power, the sealed cable module must be driven from an external SMPS.

For review we received a 1.10 meter DREi Duo cable with gold-plated RCA terminations. The 'Duo' designation points at the use of one module for both channels. Other options are XLR terminations and dual-mono modules. The proprietary circuitry is enclosed in a black aluminum box of 9 x 3.5. x 5.5cm dimensions. One power inlet connects to the SMPS, a power thru-put offers daisy-chaining for up to 10 DREi modules so only one power supply is required.